1. Field of the Invention
The present invention relates to a bicycle crank fixing structure that fixes a crank to a crank axle. More specifically, the present invention relates to a bicycle crank fixing structure in which a crank having a mounting hole and a slit extending radially from the mounting hole toward a free end of the crank is fixedly coupled to the crank axle by coupling the crank axle to the mounting hole of the crank.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One component that has been extensively redesigned is the bicycle crank axle assembly.
A bicycle crank axle assembly, which is often called a bottom bracket, is usually mounted on a hanger part of a bicycle. A conventional crank axle assembly includes the first and second axle supporting members screwed on both axial ends of the hanger part separately. The first and second axle supporting members include first and second bearing retaining sections, respectively so that first and second bearings are disposed on the first and second bearing retaining sections of the first and second axle supporting members, and a crank axle is supported on the first and second bearings. Two (right and left) cranks are non-rotatably mounted on the axial end portions of the crank axle.
One example of a conventional crank axle assembly is disclosed in Japanese Laid-Open Patent Publication No. 2004-249770 which has a right gear crank is secured on the right axial end of the crank axle. A left crank includes a mounting hole where the crank axle passes through and a slit that extends radially from the mounting hole in a crank axle mounting part of the left crank. The left crank is fastened on the crank axle by tightening up the slit by two screw members disposed to perpendicularly intersect with the slit, and by a fastening bolt screwed to the inner circumference surface of the left axial end of the crank axle. The screw members are arranged to tightly secure the left crank. These two screw members are inserted from different directions from each other to reduce the increase of thickness of the crank axle mounting part in the axial direction by preventing the interference between head portions of the screw members. In addition, the inner rings of the first and second bearings are pressed by the inner edge parts of the right and left cranks and disposed so as to enable them to be pressed by the right and left cranks.
In such conventional crank axle assembly as described above, when the crank is mounted on the crank axle by the fastening bolt, the right and left cranks contact the outside surface of the inner rings of the first and second bearings, respectively, and press the inner rings inwardly. Thus, misalignment of the first and second bearings can be eliminated by adjusting the bearing play with adjustment of the pressure imparted from the left and right cranks. After the bearing play is adjusted, the screw members are fastened to completely fixedly couple the crank to the crank axle.
Since the left crank is fixed on the crank axle by the fastening bolt and the screw members in the conventional crank axle assembly, changes in the bearing play or misalignment of the crank axle assembly will not occur unless the fastening bolt and the screw members are all loosened. However, if the fastening bolt is dropped off in a state in which the screw members are loose, there is a possibility that the left crank is detached from the crank axle. If the left crank is fixed by only the screw members without using the fastening bolt, the left crank may be detached by only loosening the screw members.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved bicycle crank fixing structure. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.